Pete,
When I was in junior high school I was told by my chorus instructor not to sing but to mouth the words. The irony of it is that I'm making a living singing.

In high school I got terrible grades in my harmony class also. I make a living playing music.

Getting a good voice teacher does help a lot.

The most important thing in my book is find material that you are committed to...that you love...and sing that. Do only the songs you love. You'll be all right.

Frank